Photo-electric relay apparatus



Dec. 12, 1933. w. D. COCKRELL PHOTO ELECTRIC RELAY APPARATUS Filed April 28, 1932 Patented Dec. 12, 1933 UNI-TED STATES 1,939,435 PHOTO-ELECTRIC RELAY APPARATUS William D. Cockrell, Schenectady, N. Y., assignor toGeneral Electric Company, a corporation of New York Application April 28, 1932. Serial No. 608,087 g 3 Claims.

My invention relates to photo-electric relay apparatus including a photo-electric device and an amplifier therefor, and an object of my invention is the provision of improved apparatus of this character which permits of very close adjustment and which allows the use of relatively long leads to the photo-electric device without sacrifice of efficiency. 7

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the single figure of the drawing which represents one embodiment of my invention, the transformer 1 is represented as having a primary 2 which may be connected with any suitable source of alternating current, for example, a 110 volt, 60 cycle commercial lighting circuit. The transformer secondary is represented as being divided into three windings 3, 4, and 5, winding 3 being the grid bias winding to which the photo-electric device is connected, 4 being the anode and load circuit supply winding, and 5 being the cathode heating winding. Winding 4 connects in the usual manner with the cathode and anode of the electron discharge amplifier 6 through resistance '7 across which connects the output or load circuit 8. The photo-electric device 10, such for example as a photo-electric tube having a cathode'll and an anode 12 connects through the leads 14 and 15 with the winding 3, lead 4 being connected directly therewith While lead 5 connects through the capacitor 16 and the grid resistor 17, that end of the winding 3 to which lead 15 connects being grounded as shown at 18. Grid 20 of amplifier 6 connects with the lead 15 at 21 and cathode 22 connects through the midpoint of winding 5 with the adjustable connection 23 of potentiometer 24 which is bridged across winding 3. In order to sheet a very close adjustment in the ratio of the voltages on each side of the connection 23 of potentiometer 24 I have provided a variable resistance connection between the connection of lead 14 and the adjacent end of the potentiometer. This is represented by the adjustable connection 25. By this arrangement it will be seen that as connection 23 is moved further toward the grounded side of the potentiometer the adjustment of the grid voltage becomes more critical but it will also be seen that the action of the adjustable connection 25 becomes finer and thus there is a compensating action.

With apparatus of this character it has been found that for the most satisfactory operation of fifi the photo-electric device a capacitor should be employed in the connection between the grid lead,

namely, lead 15 in the present case, and the secondary winding 3. If the value of this capacitor is materially above or below a certain limited range of values the sensitiveness of the apparatus is materially impaired. It is also known that where relatively long leads are employed for the connection of the photo-electric device the capacitance between the leads seriously aiTects the operation of the apparatus.

In accordance with my invention I substantially eliminate the capacitance between the photo-tube leads by providing an interposed member and utilize the capacitance between the grid lead and that member in the circuit of the apparatus. Preferably I employ for the grid lead 15 the best commercial insulated wire obtainable while for the other lead 14 ordinary commercial cable may be used. Lead 14 I enclose in a metal covering shown at 2'7 and connect this metal covering with that side of winding 3 which is grounded. For mechanical protection to the leads 14 and 15 I preferably enclose them in metal armor shown at 28, which also is grounded, and in the drawing is shown included in the ground connection 29 of the covering 2'7. By reason of the grounded covering 27 substantially all capacitance between the leads 14 and 15 is eliminated. However, there is a certain amount of capacitance between the grid lead 15 and ground, the amount of which depends upon the length of the leads 14 and 15. Since, as has been pointed out above, the capacitance between the grid lead and ground should remain within a relatively narrow range, I supplement the capacitance to ground oflead 15 by the capacitor 16 of appropriate value so that the total capacitance shall amount to the desired value for most sensitive operation of the apparatus. The value of the capacitor 16, therefore, will in general be governed by the length of the photo tube leads. Thus I am able to gain flexibilty in the location of the photo tube without sacrificing sensitivity of the apparatus. The photo tube leads accordingly may be made of any desired length until the capacitance of the grid lead to ground is as great as the total capacitance to ground of that lead in which case capacitor 16 would be omitted.

I have chosen the particular embodiment de- 105 scribed above as illustrative of my invention, and it will be apparent that various other modifications'may be made without departing from the spirit and scope of my invention, which modifications I aim to cover by the appended claims. 11C

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of alternating current supply, a photo-electric device connected to be supplied therefrom and having connecting leads, an electron discharge amplifier for said device having a grid connected with one of said leads, means for substantially eliminating capacitance between said leads and -acapacitor arranged'to supplement the capacitance between said one lead and said means.

2. In combination, a source of alternating current supply, a photo-electric device, leads connecting the device with said source, an electron discharge amplifier for said device having a grid connected with one of said leads, a conducting member between said leads and connected with one side of said source for substantially eliminating capacitance between the leads, and a capacitor between said one lead and said one side of the source to supplement the capacitance between the conducting member and the grid connected lead.

3. In combination, a source of alternating current supply, a photo-electric tube having a pair of connecting leads connected with the respective sides of said source, an electron discharge amplifier for said tube having a grid connected with one of said leads, a conducting sheath surrounding the other of said leads and connected with that side of the source to which the grid lead connects, and a capacitor in the connection between said grid connected lead and the source for supplementing the capacitance between that lead and the sheath.

- WILLIAM D. COCKRELL. 

